1. Field of the Invention
The present invention relates to a disk drive control method and apparatus, and more particularly, to a torque constant correction method and apparatus in a disk drive using a multiple sinusoidal seek servo scheme.
2. Description of the Related Art
The related art of the present invention is disclosed in Korean Laid-Open Patent No. 2001-62386 and U.S. Pat. No. 5,465,035. Korean Laid-Open Patent No. 2001-62386 teaches a technique for reducing a seek noise and increasing a seek velocity with a seek acceleration waveform constructed with a generalized Fourier series determined using a minimum mean-square error (MMSE) scheme. U.S. Pat. No. 5,465,035 teaches a technique for increasing a seek velocity and minimizing device resonance based on a modified Bang-Bang seek scheme.
A disk drive includes magnetic transducers for reading and writing information by sensing magnetic fields of disks and magnetizing the disks, respectively. The information is written in sectors along circular tracks on disk surfaces. The circular tracks are identified by track numbers. A group of tracks vertically located on the disks are collectively referred to as a cylinder. Accordingly, a track may be identified by a cylinder number.
Each transducer is typically integrated in a slider which is incorporated into a head gimbal assembly (HGA). Each HGA is attached to an actuator arm. The voice coil is located adjacent to a magnetic assembly to define a voice coil motor (VCM). The disk drive includes a driving circuit for applying a current to excite the VCM and a controller. The excited VCM rotates the actuator arm to move the transducer across the disk surface.
When the information is read/written, the disk drive may operate a seek routine which directs the transducer to move from one cylinder to the other cylinder. During the operation of the seek routine, the VCM is excited by a current used to move the transducer to a new position on the disk surface. In addition, the controller operates a servo routine which ensures the transducer moves to the accurate cylinder and center of the track.
Many kinds of disk drives use a “Bang-Bang” control algorithm to move the transducer to their accurate position in the shortest time. Typically, a square wave form current is used for a seek routine using the “Bang-Bang” control algorithm. Since the square wave form has high-frequency harmonic components, it generates mechanical resonance in a head gimbal assembly (HGA), so that mechanical components or assemblies may be excited up to a high natural frequency. In turn, the associated remaining resonance generates an audible noise or an undesirable vibration, and there is a need for the associated extension of a stabilizing time.
In order to solve these problems, there has been developed a seek servo technique using a sinusoidal seek trajectory. Although it can reduce the audible noise compared with the “Bang-Bang” seek servo technique, the sinusoidal seek servo technique still has the problem of a long seek time.
Recently, in order to overcome the shortcomings of the sinusoidal seek servo technique, a multiple sinusoidal seek servo technique using a multiple sinusoidal trajectory has been developed. Compared with the “Bang-Bang” seek servo technique, the multiple sinusoidal seek servo technique can reduce the audible noise. In addition, compared with the single sinusoidal seek servo technique, the multiple sinusoidal seek servo technique can reduce the seek time.
In general, a torque constant of a voice coil motor (VCM) in a disk drive varies depending on an assembled state of a head disk assembly (HDA), characteristics of parts of the VCM, and gain characteristics of a digital-to-analog converter (DAC) of a VCM driver. Therefore, a design torque constant determined in a servo design stage is different from a real torque constant of a real disk drive. In order to compensate for the difference between the design and real torque constants, there is a need for a torque constant correction process. Typically, the torque constant correction process is performed at the time that the disk drive is powered on.
Conventionally, in the disk drive using the multiple sinusoidal seek servo scheme, the torque constant correction process is carried out as follows.
In the torque constant correction process, a test seek is performed based on a primary harmonic sinusoidal coefficient having the same form as that of a single sinusoidal seek trajectory which is obtained from a multiple sinusoidal seek trajectory corresponding to a length of the test seek. Next, a torque constant correction value is calculated from a ratio of a real seek driving current trajectory magnitude to a design current trajectory magnitude corresponding to a design acceleration trajectory.
Next, the torque constant correction process is performed according to a seek servo scheme using the single sinusoidal seek trajectory. After that, the process is converted into a seek servo scheme using a desired-order multiple sinusoidal seek trajectory, and the seek servo is performed.
The seek servo scheme used for the torque constant correction process is different from the seek servo scheme used to perform the data read and write operations. Therefore, there is a problem in that real design is too complicated. In addition, there is another problem in that a size of associated codes is too large.